The present invention relates to aircraft of the furtive type, i.e. to aircraft that are designed specifically to minimize their equivalent radar signature (ERS) and their infrared signature. By way of non-exclusive example, aircraft of this type are unmanned combat air vehicles (UCAVs), also known as “drones”, and because of the need for discretion (mainly in terms of ERS) they have airframes of a shape that is very flat without any vertical fin. In addition, the shape of the aircraft and the need for infrared discretion where the jet leaves the nozzle have led to the nozzle being given a so-called “two-dimensional” (or “2D”) shape with the outlet section of the nozzle being rectangular or flat in shape with an aspect ratio of width over height of the order of 3 or more.
Eliminating the vertical fin (rudder) means that the aircraft must be given some other means to control yaw. Two solutions have been investigated so far. The first consists in achieving yaw control by means of aerodynamic control surfaces placed on the wings of the aircraft (double airfoil type control surfaces). Under such circumstances, the aircraft is controlled in yaw by differential drag between the two wings of the aircraft. Another solution consists in fitting the aircraft with a steerable nozzle that enables the direction of the thrust vector to be controlled.
Nevertheless, those two solutions for providing aircraft without a vertical fin with yaw control present drawbacks in terms of control effectiveness and engine performance. The use of aerodynamic control surfaces on the wings greatly increases the overall drag of the aircraft in order to generate a sufficiently large moment about the center of gravity of the aircraft. Similarly, yaw control systems that operate by steering thrust at the nozzle, in particular those that rely on injecting fluid over the side walls of the nozzle, do not enable yaw moments of sufficient magnitude to be obtained, in particular because of the very flat shape of the nozzle, which is not favorable to deflecting the thrust vector in yaw. Furthermore, mechanical systems for steering the nozzle, and consequently the thrust, are highly penalizing in terms of weight and bulk.
Finally, the above-described yaw control systems generally have an impact on the thrust performance of the engine.